Telephone and other communication systems often include a central office that serves as a hub that allows for individual users to connect to a broader communication network that includes other central offices. Such central offices can provide support for a variety of user applications including telephone service, digital subscriber line (DSL) service, etc.
FIG. 1 provides a graphical representation of a representative connection between a user and the central office. The central office includes a multiplexer or other switching device that provides a plurality of individual connections to some of the users supported by the central office. For a DSL application, the multiplexer may be a digital subscriber line access multiplexer (DSLAM) that provides DSL support for a plurality of users. Each user is connected to the central office via a local loop, which may be one or more pairs of wires that extend from the central office to the user's premises. At the customer's premises the local loop connects to a variety of customer equipment, such as telephones, computer modems, etc.
The local loop is subject to impairments. Some impairments are due to the natural environment (such as water, lightning, or electrical interference). Other impairments are due to the design of the network (such as bridge taps or load coils). Yet other impairments are due to errors made during the normal maintenance of the telecommunications network (such as incorrectly splicing pairs of wire together). All of these impairments impede the ability to provide telecommunication services; as an example, in the DSLAM application, load coils prevent the customer from using DSL at all while bridge taps reduce the bandwidth available (that is, the quality of the service) to the customer. Thus, the ability to test a customer's loop is very important to a telecommunications service provider.
Equipment that can test the customer loop is very expensive. Further, this test equipment in its normal operation inhibits the use of the customer loop for its intended purpose of providing telecommunications services. As a consequence, telecommunications service providers do not wish to deploy test equipment that is always coupled to all customer' loops. Rather, the service providers install sufficient test equipment to be able to test a reasonable subset of the customer loops and that can be selectively coupled to customer loops. This test equipment is installed in the central office nearest the customer.
Providing access to the local loop at the central office for test purposes may be referred to as providing metallic test access (MTA). The testing performed on the local loop using the MTA may include checking continuity, resistance, and other related electrical characteristics of the loop.
As the telecommunications networks have matured, regulatory agencies across the world have mandated that Incumbant Local Exchange Carriers (ILECs) provide the opportunity for Competitive Local Exchange Carriers (CLECs) to install telecommunications service equipment in central offices and provide competitive services. Naturally, CLECs must pay the ILECs for the space and power that their equipment consumes
In prior art systems, isolating the local loop for tests either required a physical disconnection of the local loop from the telecommunications service circuitry and reconnection to the testing circuitry, or the inclusion of some type of access circuitry interspersed between the telecommunications service circuitry and the local loop. Manually reconnecting customer loops to perform testing is very expensive, not to mention error prone. As a result, dedicated equipment is used to provide the access circuitry. Network operators found it convenient to split the MTA access circuitry into separate functional units. The units that would be used to implement MTA within the central office can be (without loss of generality) referred to as a test head (TH) and metallic test access unit (MTAU), where the test head performs testing using the MTAU to couple to local loops. The test head which operates on a small number of ports is physically much smaller than the MTAU, as the MTAU operates on all possible local loops while maintaining all relevant telecommunication safety standards.
Having to include such dedicated circuitry between the telecommunications service circuitry and the local loop adds significant cost to the system, in terms of power used and implementation space. Furthermore, such dedicated access circuitry increases storage space requirements as it can add additional components to the rack of equipment included within the multiplexer. Also, this additional circuitry requires maintenance of its own. Particularly (but not exclusively) in the CLEC environment, these additional costs make providing cost effective service difficult.
Therefore, a need exists for a method and apparatus for providing metallic test access within telecommunications service equipment (such as DSLAM) that can be integrated with other portions of the telecommunications service equipment such that the added overhead is minimized.